path: root/Documentation/atomic_ops.txt
diff options
Diffstat (limited to 'Documentation/atomic_ops.txt')
1 files changed, 12 insertions, 19 deletions
diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index d9ca5be9b471..68542fe13b85 100644
--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -285,15 +285,13 @@ If a caller requires memory barrier semantics around an atomic_t
operation which does not return a value, a set of interfaces are
defined which accomplish this:
- void smp_mb__before_atomic_dec(void);
- void smp_mb__after_atomic_dec(void);
- void smp_mb__before_atomic_inc(void);
- void smp_mb__after_atomic_inc(void);
+ void smp_mb__before_atomic(void);
+ void smp_mb__after_atomic(void);
-For example, smp_mb__before_atomic_dec() can be used like so:
+For example, smp_mb__before_atomic() can be used like so:
obj->dead = 1;
- smp_mb__before_atomic_dec();
+ smp_mb__before_atomic();
It makes sure that all memory operations preceding the atomic_dec()
@@ -302,15 +300,10 @@ operation. In the above example, it guarantees that the assignment of
"1" to obj->dead will be globally visible to other cpus before the
atomic counter decrement.
-Without the explicit smp_mb__before_atomic_dec() call, the
+Without the explicit smp_mb__before_atomic() call, the
implementation could legally allow the atomic counter update visible
to other cpus before the "obj->dead = 1;" assignment.
-The other three interfaces listed are used to provide explicit
-ordering with respect to memory operations after an atomic_dec() call
-(smp_mb__after_atomic_dec()) and around atomic_inc() calls
A missing memory barrier in the cases where they are required by the
atomic_t implementation above can have disastrous results. Here is
an example, which follows a pattern occurring frequently in the Linux
@@ -487,12 +480,12 @@ Finally there is the basic operation:
Which returns a boolean indicating if bit "nr" is set in the bitmask
pointed to by "addr".
-If explicit memory barriers are required around clear_bit() (which
-does not return a value, and thus does not need to provide memory
-barrier semantics), two interfaces are provided:
+If explicit memory barriers are required around {set,clear}_bit() (which do
+not return a value, and thus does not need to provide memory barrier
+semantics), two interfaces are provided:
- void smp_mb__before_clear_bit(void);
- void smp_mb__after_clear_bit(void);
+ void smp_mb__before_atomic(void);
+ void smp_mb__after_atomic(void);
They are used as follows, and are akin to their atomic_t operation
@@ -500,13 +493,13 @@ brothers:
/* All memory operations before this call will
* be globally visible before the clear_bit().
- smp_mb__before_clear_bit();
+ smp_mb__before_atomic();
clear_bit( ... );
/* The clear_bit() will be visible before all
* subsequent memory operations.
- smp_mb__after_clear_bit();
+ smp_mb__after_atomic();
There are two special bitops with lock barrier semantics (acquire/release,
same as spinlocks). These operate in the same way as their non-_lock/unlock